<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            margin: 0;
        }
        
        html,
        body {
            overflow: hidden;
        }
        
        #vas {
            background-color: #eee;
            margin: 0 auto;
            display: block;
        }
    </style>
</head>

<body>
    <canvas id="vas" width="500" height="500"></canvas>
    <script src="./demo.js"></script>
</body>

</html>